Patent specification U.S. Pat. No. 4,862,913 describes a check valve having a valve body confining a valve element. Such valves are intended to be installed into the end of a conduit to inhibit retrograde, i.e. reverse, flow of fluid within the conduit. To ensure that fluid cannot by-pass the valve, a sufficiently strong seal must be formed between the valve body and the conduit. This is achieved by making the valve body slightly larger in diameter than the conduit and forming the conduit from a resiliently flexible material. Consequently, this arrangement is unsuitable for use in systems where the fluids used are corrosive and/or of high temperatures and/or pressures. Additionally it is difficult to integrate these devices into compression fitted systems as the valve's proximity to the end of the conduit leads to damage of the valve when the ferrule is compressed, and also because the conduit is liable to significantly deform when the ferrule is tightened compromising the effectiveness of the seal at the joint. Another example of an insert check valve is part number #110 manufactured by Smart Products Inc. of 675 Jarvis Drive, Morgan Hill, Calif. 95037 USA http://www.smartproducts.com.
Patent specification U.S. Pat. No. 6,981,512 relates to a biased-ball check valve assembly. The central position of the valve ball relative to the conduit's ends lends itself more easily for adaptation with compression fitting systems. However, the ball valve does not provide the necessary protection against reverse flow where precise control of fluid flow is required, such as in gas manifolds and systems for the control of supply/removal of reagents/products in chemical reactors.